Fuel injection control device

ABSTRACT

A fuel injection control device includes a valve closing detection unit ( 54 ) to detect a valve closing timing by using either of an electromotive force quantity detection mode and a timing detection mode, a selection unit ( 21 ) to select either of the electromotive force quantity detection mode and the timing detection mode for detecting the valve closing timing, and a correction unit ( 21 ) to calculate a correction coefficient for correcting a requested injection quantity so as to reduce the difference between an estimated injection quantity and the requested injection quantity, and the selection unit selects the electromotive force quantity detection mode regardless of the value of the requested injection quantity when the calculation of the correction coefficient is not completed.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2016-93316filed on May 6, 2016, the disclosure of which is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a fuel injection control device havinga fuel injection valve of an electromagnetically driven type.

BACKGROUND ART

A fuel injection control device controls injection through a fuelinjection valve of an electromagnetically driven type incorporated in aninternal combustion engine. Specifically, a fuel injection controldevice calculates a requested injection quantity in response to theoperational status of an internal combustion engine and conducts a coilby an injection command pulse of a pulse width corresponding to therequested injection quantity. As a result, a magnetic attraction forceis generated in the coil, a valve body of a fuel injection valve isdriven to valve opening, and a fuel is controlled so as to be injectedby the requested injection quantity.

In a fuel injection valve of a direct-injection type that injects a fuelof a high pressure directly into a cylinder however, the linearity ofthe change characteristic of an actual injection quantity to the pulsewidth of an injection command pulse tends to deteriorate in a partiallift region. The partial lift region means a region of a partial liftstate where an injection command pulse width is short and the liftquantity of a valve body does not reach a full lift position. In such apartial lift region, the variation of the lift quantity of a valve bodyincreases and the variation of an injection quantity tends to increase.If the variation of an injection quantity increases, exhaust emissionand drivability may deteriorate undesirably.

In a partial lift region, the variation of the lift quantity of a valvebody is large and hence the variation of time from the start of valveclosing to the finish of the valve closing is also large. When thetiming of valve closing by a valve body can be detected in a partiallift region however, deviation between an injection command pulse from afuel injection control device and actual valve behavior can berecognized by the fuel injection control device. Consequently, it ispossible to correct an injection command pulse on the basis of thedeviation and control an injection quantity. A technology of detectingthe timing of valve closing is disclosed accordingly.

In a fuel injection valve, an induced electromotive force is generatedin a coil in proportion to the displacement of a valve body after aninjection command pulse is turned off. Since a terminal voltage of thefuel injection valve varies by the generated induced electromotive forcetherefore, the induced electromotive force can be detected. Two modes ofdetecting the timing of valve closing by using such an inducedelectromotive force generated in a coil are disclosed. In PatentLiterature 1, as the detection of an induced electromotive forcequantity, the difference of an induced electromotive force quantitygenerated during valve closing caused by the difference of a liftquantity is detected. In Patent Literature 2, as timing detection, aninflection point of an induced electromotive force responding to thedrive variation of a movable core after a valve body is seated isdetected by using a terminal voltage.

PRIOR ART LITERATURES Patent Literature

Patent Literature 1: JP2015-96720A

Patent Literature 2: WO2013/191267A

SUMMARY OF INVENTION

When induced electromotive force quantity detection and timing detectionare compared, the detection range in the induced electromotive forcequantity detection is wider. In the timing detection, a lift quantity ofa certain extent is required for generating an inflection point andhence a timing of valve closing cannot be detected by the timingdetection when the lift quantity is small.

Further, when induced electromotive force quantity detection and timingdetection are compared, the detection accuracy in the timing detectionis superior. In the induced electromotive force quantity detection, anelectromotive force quantity tends to be influenced by externaldisturbance and hence the detection accuracy may deteriorateundesirably. In the timing detection, an inflection point is detectedand hence the detection accuracy is superior.

In this way, when induced electromotive force quantity detection andtiming detection are compared, they have advantages and disadvantagesrespectively and hence it is desirable to detect a timing of valveclosing by both of the detection modes simultaneously. In order toexecute both of the detection modes however, processing capabilitieshave to be increased and the implementation scale of a control devicemay increase undesirably.

An object of the present disclosure is to provide a fuel injectioncontrol device capable of securing both of detection accuracy anddetection range while the upsizing of the control device is suppressed.

According to an aspect of the present disclosure, the fuel injectioncontrol device includes a valve closing detection unit to detect a valveclosing timing by using either of an electromotive force quantitydetection mode and a timing detection mode, a selection unit to selecteither of the electromotive force quantity detection mode and the timingdetection mode for detecting the valve closing timing, and a correctionunit to calculate a correction coefficient for correcting a requestedinjection quantity so as to reduce the difference between an estimatedinjection quantity and the requested injection quantity. The selectionunit selects the electromotive force quantity detection mode regardlessof a value of the requested injection quantity when the calculation ofthe correction coefficient is not completed.

According to the present disclosure, the valve closing detection unitcan execute either of the induced electromotive force quantity detectionmode and the timing detection mode. Consequently, the valve closingdetection unit can be downsized further than a configuration ofexecuting both of the modes simultaneously. Further, the selection unitselects the timing detection mode when the requested injection quantityis larger than the reference injection quantity and selects theelectromotive force quantity detection mode when the requested injectionquantity is smaller than the reference injection quantity. The timingdetection mode is superior to the electromotive force quantity detectionmode in detection accuracy but has a detection range smaller than theelectromotive force quantity detection mode. In the case of thereference injection quantity or more that is in the detection range ofbeing detectable by the timing detection mode therefore, it is possibleto select the timing detection mode and use the timing detection modesuitably. Further, in the case of less than the reference injectionquantity that is in the detection range of not being detectable by thetiming detection mode, the electromotive force quantity detection modeis selected. Consequently, the electromotive force quantity detectionmode can make up for the narrow detection range of the timing detectionmode. As a result, a fuel injection device that can secure both of thedetection accuracy and the detection range of a valve closing timing canbe materialized.

Further, in the present disclosure, a correction coefficient iscalculated so as to reduce the difference between an estimated injectionquantity estimated by using a valve closing timing detected by anelectromotive force quantity detection mode and a requested injectionquantity. Then a selection unit uses a value corrected by the correctioncoefficient for a requested injection quantity of determining whether ornot a timing detection mode is selected. Then the selection unit selectsnot the timing detection mode but the electromotive force quantitydetection mode when the calculation of the correction coefficient is yetto be completed. Since the detection range of the timing detection modeis narrow as stated earlier, when the difference between a requestedinjection quantity and an actual injection quantity is large while thetiming detection mode is used, the actual injection quantity may not bein the detection range of the timing detection mode undesirably.Consequently, in order to reduce the difference between a requestedinjection quantity and an actual injection quantity, firstly therequested injection quantity is corrected by using an estimatedinjection quantity estimated by using a valve closing timing of theelectromotive force quantity detection mode having a wide detectionrange. As a result, the difference between the requested injectionquantity and an actual injection quantity can be reduced and thus theactual injection quantity can be in the detection range of the timingdetection mode. It is therefore possible to switch the electromotiveforce quantity detection mode and the timing detection mode underappropriate conditions and make use of the mutual advantages of both thedetection modes while erroneous detection by the timing detection modeis suppressed.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a view showing a fuel injection system according to a firstembodiment;

FIG. 2 is a sectional view showing a fuel injection valve;

FIG. 3 is a graph showing a relationship between a conduction time andan injection quantity;

FIG. 4 is a graph showing the behavior of a valve body;

FIG. 5 is a graph showing a relationship between a voltage and adifference;

FIG. 6 is a flowchart showing selection processing;

FIG. 7 is a graph for explaining a detection range; and

FIG. 8 is a flowchart showing correction processing.

DESCRIPTION OF EMBODIMENTS First Embodiment

A first embodiment according to the present disclosure is explained inreference to FIGS. 1 to 8. A fuel injection system 100 shown in FIG. 1includes a plurality of fuel injection valves 10 and a fuel injectioncontrol device 20. The fuel injection control device 20 controls theopening and closing of the fuel injection valves 10 and controls fuelinjection into a combustion chamber 2 of an internal combustion engineE. The fuel injection valves 10: are installed in an internal combustionengine E of an ignition type, for example a gasoline engine; and injecta fuel directly into a plurality of combustion chambers 2 of theinternal combustion engine E respectively. A mounting hole 4 penetratingconcentrically with an axis C of a cylinder is formed in a cylinder head3 constituting the combustion chamber 2. A fuel injection valve 10 isinserted into and fixed to the mounting hole 4 so that the tip may beexposed into the combustion chamber 2.

A fuel supplied to the fuel injection valve 10 is stored in a fuel tanknot shown in the figure. The fuel in the fuel tank is pumped up by alow-pressure pump 41, the fuel pressure is raised by a high-pressurepump 40, and the fuel is sent to a delivery pipe 30. The high-pressurefuel in the delivery pipe 30 is distributed and supplied to the fuelinjection valve 10 of each cylinder. A spark plug 6 is attached to aposition of the cylinder head 3 facing the combustion chamber 2.Further, the spark plug 6 is arranged in a vicinity of the tip of thefuel injection valve 10.

The configuration of the fuel injection valve 10 is explained hereunderin reference to FIG. 2. As shown in FIG. 2, the fuel injection valve 10includes a body 11, a valve body 12, a drive coil 13, a stator core 14,a movable core 15, and a housing 16. The body 11 comprises a magneticmaterial. A fuel passage 11 a is formed in the interior of the body 11.

Further, the valve body 12 is contained in the interior of the body 11.The valve body 12 comprises a metal material and is formed cylindricallyas a whole. The valve body 12 can be displaced reciprocally in an axialdirection in the interior of the body 11. The body 11 is configured soas to have an injection hole body 17 in which a valve seat 17 b wherethe valve body 12 is seated and an injection hole 17 a to inject a fuelare formed at the tip part.

The injection hole 17 a is formed at the tip part of the body 11inserted into the combustion chamber 2 in the insertion direction. Thetip part of the body 11 is formed conically or hemispherically. Theinjection hole 17 a includes a plurality of holes formed radially fromthe inside toward the outside of the body 11. A fuel of a high pressureis injected into the combustion chamber 2 through the injection hole 17a. The fuel is vaporized by passing through the injection hole 17 a andis in the state of being likely to be mixed with air.

The main body part of the valve body 12 has a columnar shape. The tippart of the valve body 12 has a conical shape extending from the tip ofthe main body part on the side of the injection hole 17 a toward theinjection hole 17 a. The part, which is seated on the valve seat 17 b,of the valve body 12 is a seat surface 12 a. The seat surface 12 a isformed at the tip part of the valve body 12.

When the valve body 12 is operated for valve closing so as to seat theseat surface 12 a on the valve seat 17 b, fuel injection from theinjection hole 17 a is stopped. When the valve body 12 is operated forvalve opening so as to separate the seat surface 12 a from the valveseat 17 b, a fuel is injected through the injection hole 17 a.

The drive coil 13 is an actuator and gives a magnetic attraction forceto the movable core 15 in a valve opening direction. The drive coil 13is configured by being wound around a resin-made bobbin 13 a and issealed by the bobbin 13 a and a resin material 13 b. In other words, acoil body of a cylindrical shape includes the drive coil 13, the bobbin13 a, and the resin material 13 b. The bobbin 13 a is inserted over theouter peripheral surface of the body 11.

The stator core 14 is a stator and is fixed to the body 11. The statorcore 14 comprises a magnetic material and is formed cylindrically. Afuel passage 14 a is formed in the interior of the cylinder of thestator core 14. The stator core 14 is inserted at a position opposite tothe bobbin 13 a over the inner peripheral surface of the body 11.

Further, the outer peripheral surface of the resin material 13 b to sealthe drive coil 13 is covered with the housing 16. The housing 16comprises a metallic magnetic material and is formed cylindrically. Alid member 18 comprising a metallic magnetic material is attached to anopening end part of the housing 16. Consequently, the coil body issurrounded by the body 11, the housing 16, and the lid member 18.

The movable core 15 is a mover and is retained by the valve body 12relatively displaceably in the direction of driving the valve body 12.The movable core 15 comprises a metallic magnetic material, is formeddiscoidally, and is inserted over the inner peripheral surface of thebody 11. The body 11, the valve body 12, the coil body, the stator core14, the movable core 15, and the housing 16 are arranged so that thecenter lines of them may coincide with each other. Then the movable core15 is arranged on the side of the stator core 14 closer to the injectionhole 17 a and faces the stator core 14 in the manner of having aprescribed gap from the stator core 14 when the drive coil 13 is notconducted.

The body 11, the housing 16, the lid member 18, and the stator core 14,which surround the coil body: comprise magnetic materials as statedearlier; and hence form a magnetic circuit acting as a pathway of amagnetic flux generated when the drive coil 13 is conducted.

As shown in FIG. 1, the outer peripheral surface of a part of the body11 located on the side closer to the injection hole 17 a than thehousing 16 is in contact with an inner peripheral surface 4 b of themounting hole 4 on the lower side. Further, the outer peripheral surfaceof the housing 16 forms a gap from an inner peripheral surface 4 a ofthe mounting hole 4 on the upper side.

A through hole 15 a is formed in the movable core 15 and, by insertingthe valve body 12 into the through hole 15 a, the valve body 12 isassembled to the movable core 15 slidably and relatively movably. Alocking part 12 d formed by expanding the diameter from the main bodypart is formed at an end part, which is located on the upper side inFIG. 2, of the valve body 12 on the side opposite to the injection hole.When the movable core 15 is attracted by the stator core 14 and movesupward, the locking part 12 d moves in the state of being locked to themovable core 15 and hence the valve body 12 also moves in response tothe upward movement of the movable core 15. Even in the state ofbringing the movable core 15 into contact with the stator core 14, thevalve body 12 can move relatively to the movable core 15 and can liftup.

A main spring SP1 is arranged on the side of the valve body 12 oppositeto the injection hole and a sub spring SP2 is arranged on the side ofthe movable core 15 closer to the injection hole 17 a. The main springSP1 and the sub spring SP2 are coil-shaped and deform resiliently in anaxial direction. A resilient force of the main spring SP1 is given tothe valve body 12 in the direction of valve closing that is the downwarddirection in FIG. 2 as a counter force coming from an adjustment pipe101. A resilient force of the sub spring SP2 is given to the movablecore 15 in the direction of attracting the movable core 15 as a counterforce coming from a recess 11 b of the body 11.

In short, the valve body 12 is interposed between the main spring SP1and the valve seat 17 b and the movable core 15 is interposed betweenthe sub spring SP2 and the locking part 12 d. Then the resilient forceof the sub spring SP2 is transferred to the locking part 12 d throughthe movable core 15 and is given to the valve body 12 in the directionof valve opening. It can also be said therefore that a resilient forceobtained by subtracting a sub resilient force from a main resilientforce is given to the valve body 12 in the direction of valve closing.

Here, the pressure of a fuel in the fuel passage 11 a is applied to thewhole surface of the valve body 12 but a force of pushing the valve body12 toward the valve closing side is larger than a force of pushing thevalve body 12 toward the valve opening side. The valve body 12 thereforeis pushed by the fuel pressure in the direction of valve closing. Duringvalve closing, the fuel pressure is not applied to the surface of a partof the valve body 12 located on the downstream side of the seat surface12 a. Then along with valve opening, the pressure of a fuel flowing intothe tip part increases gradually and a force of pushing the tip parttoward valve opening side increases. The fuel pressure in the vicinityof the tip part therefore increases in accordance with the valve openingand resultantly the fuel pressure valve closing force decreases. For theabove reason, the fuel pressure valve closing force is maximum duringvalve closing and reduces gradually as the degree of the movement of thevalve body 12 toward valve opening increases.

The behavior of the drive coil 13 by conduction is explained hereunder.When the drive coil 13 is conducted and an electromagnetic attractionforce is generated in the stator core 14, the movable core 15 isattracted toward the stator core 14 by the electromagnetic attractionforce. The electromagnetic attraction force is also called anelectromagnetic force. As a result, the valve body 12 connected to themovable core 15 operates for valve opening against the resilient forceof the main spring SP1 and the fuel pressure valve closing force. On theother hand, when the conduction of the drive coil 13 is stopped, thevalve body 12 operates for valve closing together with the movable core15 by the resilient force of the main spring SP1.

The configuration of the fuel injection control device 20 is explainedhereunder. The fuel injection control device 20 is operated by anelectronic control unit (called ECU for short). The fuel injectioncontrol device 20 includes a control circuit 21, a booster circuit 22, avoltage detection unit 23, a current detection unit 24, and a switchunit 25. The control circuit 21 is also called a microcomputer. The fuelinjection control device 20 receives information from various sensors.For example, a fuel pressure supplied to the fuel injection valve 10 isdetected by a fuel pressure sensor 31 attached to the delivery pipe 30and the detection result is given to the fuel injection control device20 as shown in FIG. 1. The fuel injection control device 20 controls thedrive of the high-pressure pump 40 on the basis of the detection resultof the fuel pressure sensor 31.

The control circuit 21 includes a central processing unit, anon-volatile memory (ROM), a volatile memory (RAM), and the like andcalculates a requested injection quantity and a requested injectionstart time of a fuel on the basis of a load and a machine rotationalspeed of an internal combustion engine E. The storage mediums such as aROM and a RAM are non-transitive tangible storage mediums tonon-temporarily store programs and data that are readable by a computer.The control circuit 21: functions as an injection control unit; testsand stores an injection characteristic showing a relationship between aconduction time Ti and an injection quantity Q in the ROM beforehand;controls the conduction time Ti to the drive coil 13 in accordance withthe injection characteristic; and thus controls the injection quantityQ. The conduction time Ti to the drive coil 13 is a pulse width of aninjection command pulse and is also called an injection command pulsewidth Ti.

The voltage detection unit 23 and the current detection unit 24 detect avoltage and an electric current applied to the drive coil 13 and givethe detection results to the control circuit 21. The voltage detectionunit 23 detects a minus terminal voltage of the drive coil 13. Thevoltage detection unit 23 detects the variation of an inducedelectromotive force caused by intercepting the electric current suppliedto the drive coil 13 and displacing the valve body 12 and the movablecore 15 in the valve closing direction as a voltage value. Further, thevoltage detection unit 23 detects the variation of an inducedelectromotive force caused by displacing the movable core 15 relativelyto the valve body 12 after the valve seat 17 b comes into contact withthe valve body 12 as a voltage value. A valve closing detection unit 54detects a valve closing timing when the valve body 12 operates for valveclosing by using a detected voltage.

The control circuit 21 has a charge control unit 51, a discharge controlunit 52, a current control unit 53, and the valve closing detection unit54. The booster circuit 22 and the switch unit 25 operate on the basisof an injection command pulse outputted from the control circuit 21. Theinjection command pulse is a signal to command a state of conducting thedrive coil 13 of the fuel injection valve 10 and is set by using arequested injection quantity and a requested injection start time. Theinjection command pulse includes an injection signal and a boost signal.

The booster circuit 22 applies a boosted boost voltage to the drive coil13. The booster circuit 22 has a condenser, a coil and a switchingelement and a battery voltage applied from a battery terminal of abattery 102 is boosted by the drive coil 13 and stored in the condenser.The booster circuit 22 controls the timing of boost by the chargecontrol unit 51. Further, the booster circuit 22 controls the timing ofdischarge by the discharge control unit 52. In this way, a voltage of aboosted and stored electric power corresponds to a boost voltage.

When the discharge control unit 52 turns on a prescribed switchingelement so that the booster circuit 22 may discharge, a boost voltage isapplied to the drive coil 13 of the fuel injection valve 10. Thedischarge control unit 52 turns off the prescribed switching element ofthe booster circuit 22 when stopping applying voltage to the drive coil13.

The current control unit 53 controls on or off of the switch unit 25 andcontrols the electric current flowing in the drive coil 13 by using adetection result of the current detection unit 24. The switch unit 25applies a battery voltage or a boost voltage from the booster circuit 22to the drive coil 13 in an on state and stops the application in an offstate. The current control unit 53, at a voltage application start timecommanded by an injection command pulse for example: turns on the switchunit 25; applies a boost voltage; and starts conduction. Then a coilcurrent increases in accordance with the start of the conduction. Thenthe current control unit 53 turns off the conduction when a detectedcoil current value reaches a target value on the basis of a detectionresult of the current detection unit 24. In short, the current controlunit 53 controls a coil current so as to be raised to a target value byapplying a boost voltage through initial conduction. Further, thecurrent control unit 53 controls conduction by a battery voltage so thata coil current may be maintained at a value lower than a target valueafter a boost voltage is applied.

As shown in FIG. 3, in a full lift region where an injection commandpulse width is comparatively long, the lift quantity of the valve body12 reaches a full lift position, namely a position where the movablecore 15 abuts on the stator core 14. In a partial lift region where aninjection command pulse width is comparatively short however, a partiallift state where the lift quantity of the valve body 12 does not reach afull lift position, namely a state before the movable core 15 abuts onthe stator core 14, is caused.

The fuel injection control device 20, in a full lift region, executesfull lift injection of driving the fuel injection valve 10 for valveopening by an injection command pulse allowing the lift quantity of thevalve body 12 to reach a full lift position. Further, the fuel injectioncontrol device 20, in a partial lift region, executes partial liftinjection of driving the fuel injection valve 10 for valve opening by aninjection command pulse causing a partial lift state where the liftquantity of the valve body 12 does not reach a full lift position.

A detection mode of the valve closing detection unit 54 is explainedhereunder in reference to FIG. 4. The graph at the upper part in FIG. 4shows a waveform of minus terminal voltage of the drive coil 13 afterconduction is switched from on to off and enlargedly shows a waveform offlyback voltage when conduction is switched off. The flyback voltage isa negative value and hence is shown upside down in FIG. 4. In otherwords, a waveform of voltage obtained by reversing the positive andnegative is shown in FIG. 4.

The valve closing detection unit 54: can execute an electromotive forcequantity detection mode and a timing detection mode; and detects a valveclosing timing when the valve body 12 shifts to valve closing by usingeither of the detection modes. The electromotive force quantitydetection mode detects a valve closing timing by comparing anaccumulated quantity of voltage values detected by the voltage detectionunit 23 and a prescribed reference quantity in order to detect a valveclosing timing in partial lift injection. The timing detection modedetects an inflection point of voltage values detected by the voltagedetection unit 23 as a valve closing timing.

Firstly, the electromotive force quantity detection mode is explained.In the fuel injection valve 10, as shown in FIG. 4, a minus terminalvoltage varies by an induced electromotive force after the time t1 whenan injection command pulse is switched off. When a waveform of detectedelectric power and a waveform of no induced electromotive force arecompared, it is obvious that a voltage increases to the extent of theinduced electromotive force in the waveform of the detected electricpower value as shown with the oblique lines in FIG. 4. An inducedelectromotive force is generated when the movable core 15 passes througha magnetic field during the time from the start of valve closing to thefinish of valve closing. Since the change rate of the valve body 12 andthe change rate of the movable core 15 vary comparatively largely andthe change characteristic of a minus terminal voltage varies at thevalve closing timing of the valve body 12, a voltage inflection pointwhere the change characteristic of a minus terminal voltage variesappears in the vicinity of the valve closing timing.

By paying attention to such a characteristic, the valve closingdetection unit 54 detects a voltage inflection point time as informationrelated to a valve closing timing as follows. The detection of a valveclosing timing shown below is executed for each of the cylinders. Thevalve closing detection unit 54 calculates a first filtered voltage Vsm1obtained by filtering (smoothing) a minus terminal voltage Vm of thefuel injection valve 10 with a first low-pass filter during theimplementation of partial lift injection at least after an injectioncommand pulse of the partial lift injection is switched off. The firstlow-pass filter uses a first frequency lower than the frequency of anoise component as the cut-off frequency. Further, the valve closingdetection unit 54 calculates a second filtered voltage Vsm2 obtained byfiltering (smoothing) the minus terminal voltage Vm of the fuelinjection valve 10 with a second low-pass filter using a secondfrequency lower than the first frequency as the cut-off frequency. As aresult, the first filtered voltage Vsm1 obtained by removing a noisecomponent from a minus terminal voltage Vm and the second filteredvoltage Vsm2 used for voltage inflection point detection can becalculated.

Further, the valve closing detection unit 54 calculates a differenceVdiff (=Vsm1−Vsm2) between the first filtered voltage Vsm1 and thesecond filtered voltage Vsm2. Furthermore, the valve closing detectionunit 54 calculates a time from a prescribed reference timing to a timingwhen the difference Vdiff comes to be an inflection point as a voltageinflection point time Tdiff. On this occasion, as shown in FIG. 5, thevoltage inflection point time Tdiff is calculated by regarding a timingwhen the difference Vdiff exceeds a prescribed threshold value Vt as atiming when the difference Vdiff comes to be an inflection point. Inother words, a time from a prescribed reference timing to a timing whena difference Vdiff exceeds a prescribed threshold value Vt is calculatedas the voltage inflection point time Tdiff. The difference Vdiffcorresponds to an accumulated value of induced electromotive forces andthe threshold value Vt corresponds to a prescribed reference quantity.As a result, the voltage inflection point time Tdiff that varies inresponse to the valve closing timing of the fuel injection valve 10 canbe calculated with a high degree of accuracy. In the present embodiment,the voltage inflection point time Tdiff is calculated by regarding thereference timing as a time t2 when the difference is generated. Thethreshold value Vt is a fixed value or a value calculated by the controlcircuit 21 in response to a fuel pressure, a fuel temperature, andothers.

In a partial lift region of the fuel injection valve 10, since aninjection quantity varies and also a valve closing timing varies by thevariation of a lift quantity of the fuel injection valve 10, there is acorrelation between an injection quantity and a valve closing timing ofthe fuel injection valve 10. Further, since a voltage inflection pointtime Tdiff varies in response to the valve closing timing of the fuelinjection valve 10, there is a correlation between a voltage inflectionpoint time Tdiff and an injection quantity. By paying attention to suchcorrelations, an injection command pulse correction routine is executedby the fuel injection control device 20 and hence an injection commandpulse in partial lift injection is corrected on the basis of a voltageinflection point time Tdiff.

The fuel injection control device 20 stores a relationship between avoltage inflection point time Tdiff and an injection quantity Qbeforehand in the control circuit 21 for each of a plurality ofinjection command pulse widths Ti in partial lift injection. Then thecontrol circuit 21 estimates an injection quantity Q corresponding to acalculated voltage inflection point time Tdiff for each of the injectioncommand pulse widths Ti by using a relationship between a voltageinflection point time Tdiff and an injection quantity Q for each of theinjection command pulse widths Ti stored in a ROM beforehand.

Further, a relationship between an injection command pulse width Ti andan injection quantity Q is set on the basis of the estimation result. Asa result, it is possible to: set a relationship between an injectioncommand pulse width Ti and an injection quantity Q corresponding to acurrent injection characteristic of the fuel injection valve 10; andcorrect the relationship between the injection command pulse width Tiand the injection quantity Q. Successively, a requested injectioncommand pulse width Tireq responding to a requested injection quantityQreq is calculated by using a map defining the relationship between theinjection command pulse width Ti and the injection quantity Q.

The timing detection mode is explained hereunder. At a moment when thevalve body 12 starts valve closing from a valve opening state and comesinto contact with the valve seat 17 b, since the movable core 15separates from the valve body 12, the acceleration of the movable core15 varies at the moment when the valve body 12 comes into contact withthe valve seat 17 b. In the timing detection mode, a valve closingtiming is detected by detecting the variation of the acceleration of themovable core 15 as the variation of an induced electromotive forcegenerated in the drive coil 13. The variation of the acceleration of themovable core 15 can be detected by a second-order differential value ofa voltage detected by the voltage detection unit 23.

Specifically, as shown in FIG. 4, after the conduction to the drive coil13 is stopped at the time t1, the movable core 15 switches from upwarddisplacement to downward displacement in conjunction with the valve body12. Then when the movable core 15 separates from the valve body 12 afterthe valve body 12 shifts to valve closing, a force in the valve closingdirection that has heretofore been acting on the movable core 15 throughthe valve body 12, namely a force caused by a load by the main springSP1 and a fuel pressure, disappears. A load of the sub spring SP2therefore acts on the movable core 15 as a force in the valve openingdirection. When the valve body 12 reaches a valve closing position andthe direction of the force acting on the movable core 15 changes fromthe valve closing direction to the valve opening direction, the increaseof an induced electromotive force that has heretofore been increasinggently reduces and the second-order differential value of a voltageturns downward at the valve closing time t3. By detecting the maximumvalue of the second-order differential value of a minus terminal voltageby the valve closing detection unit 54, a valve closing timing of thevalve body 12 can be detected with a high degree of accuracy.

Similarly to the electromotive force quantity detection mode, there is acorrelation between a valve closing time from the stop of conduction toa valve closing timing and an injection quantity. By paying attention tosuch a correlation, an injection command pulse correction routine isexecuted by the fuel injection control device 20 and thus an injectioncommand pulse in partial lift injection is corrected on the basis of thevalve closing time.

The fuel injection control device 20 stores a relationship between avalve closing time detected by the timing detection mode and aninjection quantity Q beforehand in the control circuit 21 for each of aplurality of injection command pulse widths Ti in partial liftinjection. Then the control circuit 21 estimates an injection quantity Qcorresponding to a calculated valve closing time for each of theinjection command pulse widths Ti by using a relationship between avalve closing time and an injection quantity Q for each of the injectioncommand pulse widths Ti stored in a ROM beforehand.

Further, similarly to the electromotive force quantity detection modestated earlier, a relationship between an injection command pulse widthTi and an injection quantity Q is set on the basis of the estimationresult. As a result, similarly to the electromotive force quantitydetection mode, it is possible to: set a relationship between aninjection command pulse width Ti and an injection quantity Qcorresponding to a current injection characteristic of the fuelinjection valve 10; and correct the relationship between the injectioncommand pulse width Ti and the injection quantity Q. Successively, arequested injection command pulse width Tireq responding to a requestedinjection quantity Qreq is calculated by using a map defining therelationship between the injection command pulse width Ti and theinjection quantity Q.

Selection processing of selecting a detection mode is explainedhereunder. The selection processing is executed repeatedly for a shortperiod of time in the state of the power-up of the control circuit 21.

At S1, a requested injection quantity of a fuel is calculated on thebasis of a load and a machine rotational speed of an internal combustionengine E and the process proceeds to S2. Here, the requested injectionquantity is at least a value corrected by initial correction. In otherwords, the requested injection quantity is a value that is corrected bya correction coefficient and is less different from an estimatedinjection quantity. Concrete correction processing is described later.

At S2, a maximum injection quantity and a minimum injection quantity ofa partial injection quantity are calculated and the process proceeds toS3. The partial injection quantity is an injection quantity in a partiallift region. The partial injection quantity varies by the deteriorationof the fuel injection valve 10 and the like. Then the deterioration ofthe fuel injection valve 10 and the like are addressed by reflectingcorrection ratios to the maximum injection quantity and the minimuminjection quantity, those acting as references, namely nominalcharacteristics. Specifically, at S2, the maximum injection quantity andthe minimum injection quantity in partial lift injection are correctedby using a valve closing timing stated earlier.

At S3, an injection ratio of the requested injection quantity to apartial injection quantity region is calculated and the process proceedsto S4. The partial injection quantity region is an injection rangebetween the maximum injection quantity and the minimum injectionquantity in partial lift injection. Since the maximum injection quantityand the minimum injection quantity at S2 are post-correction values thathave been corrected, the partial injection quantity region can be setwith a high degree of accuracy.

At S4, whether or not correction processing in the electromotive forcequantity detection mode is completed is determined and the processproceeds to S5 when the correction processing is completed and to S7when the correction processing is not completed. The correctionprocessing is described later in reference to FIG. 8.

At S5, the calculated injection ratio and a prescribed reference ratioare compared and the process proceeds to S6 when the calculatedinjection ratio is equal to or larger than the reference ratio and to S7when the calculated injection ratio is not equal to or larger than thereference ratio. The reference ratio is determined preferably so as tohave a hysteresis using a first threshold value and a second thresholdvalue smaller than the first threshold value. The value of the referenceratio used at S5 therefore varies by a current detection mode.Specifically, the reference ratio is set at the first threshold valuewhile the electromotive force quantity detection mode is selected andthe reference ratio is set at the second threshold value while thetiming selection mode is selected.

At S6, since a calculated injection ratio is equal to or larger than areference ratio, the timing detection mode is selected as the detectionmode and the process proceeds to S8. At S7, since the calculatedinjection ratio is smaller than the reference ratio or the correctionprocessing is not completed, the electromotive force quantity detectionmode is selected as the detection mode and the process proceeds to S8.

At S8, whether or not a selected detection mode changes from theprevious detection mode is determined and the process proceeds to S9when the selected detection mode changes and to S9 when the selecteddetection mode does not change. At S9, since the detection mode haschanged, the process waits without applying a next detection mode for acertain period of time, for example for one cycle, and the processfinishes. When the detection mode is switched in this way, the lastdetection mode before the switching is maintained until a newly selecteddetection mode is available. In other words, when a detection modechanges, the detection mode is not switched immediately, is prohibitedfrom being changed for a prescribed period of time, and is switched to anext detection mode after the lapse of the prescribed period of time.

As shown in FIG. 7, an injection time varies in response to a requestedinjection quantity. Then in a partial lift region, the detection rangeof the electromotive force quantity detection mode and the detectionrange of the timing detection mode are different from each other.Specifically, the detection range of the timing detection mode islocated on the side where a required injection quantity is larger than areference ratio in the partial lift region. The electromotive forcequantity detection mode covers from a minimum injection quantity Tmin toa value in the vicinity of a maximum injection quantity Tmax. Thedetection range of the electromotive force quantity detection modetherefore includes the detection range of the timing detection mode andis wider than the detection range of the timing detection mode. Thedetection accuracy of a valve closing timing in the timing detectionmode however is superior. As explained in FIG. 6 stated earliertherefore, the detection mode is switched on the basis of a requestedinjection quantity.

Initial correction of a requested injection quantity is explainedhereunder in reference to FIG. 8. As stated earlier, either of thetiming detection mode and the electromotive force quantity detectionmode is selected in response to a requested injection quantity. Sincethe difference between a requested injection quantity and an actualinjection quantity is caused by various factors however, it is necessaryto correct the requested injection quantity in order to bring therequested injection quantity and the actual injection quantity close toeach other. Moreover, since the requested injection quantity is in thedetection range of the timing detection mode before the requestedinjection quantity is corrected, the timing detection mode is selectedin some cases.

When a difference exists between a requested injection quantity and anactual injection quantity however, the actual injection quantity may notbe in the detection range of the timing detection mode undesirably.Consequently, it is necessary to correct the requested injectionquantity by the electromotive force quantity detection mode firstlybefore the timing detection mode is executed.

The correction processing shown in FIG. 8 is executed repeatedly for ashort period of time in the state of the power-up of the control circuit21 until the electromotive force quantity detection is determined to becompleted. At S21, a requested injection quantity of a fuel iscalculated on the basis of a load and a machine rotational speed of aninternal combustion engine E and the process proceeds to S22.

At 22, whether or not a detection condition is satisfied is determinedand the process proceeds to S23 when the detection condition issatisfied and the process finishes when the detection condition is notsatisfied. As the detection condition, a condition suitable fordetecting a valve closing timing by the electromotive force quantitydetection mode is set. The detection condition is satisfied for examplewhen an injection interval of a prescribed time or longer is secured.The reason is that an injection quantity may deviate undesirably by theinfluence of a residual magnetic force when an injection interval of aprescribed time or longer is not secured.

At S23, since the detection condition is satisfied, an estimatedinjection quantity is calculated by using a valve closing timingdetected by the electromotive force quantity detection mode and theprocess proceeds to S24. Since a voltage inflection point time Tdiffdetected by the electromotive force quantity detection mode has acorrelation with an injection quantity as stated earlier, an estimatedinjection quantity can be calculated. Further, when an estimatedinjection quantity is calculated, it is preferable to estimate theestimated injection quantity by using not only a valve closing timingbut also parameters having a correlation with an actual injectionquantity. The parameters are a fuel pressure and a conduction time forexample. The reason why a fuel pressure is used is to take the influenceof a valve opening force difference caused by the difference of the fuelpressure into consideration. The reason why a conduction time is used isto take a charged energy difference caused by the difference of theconduction time into consideration. An estimated injection quantitytherefore is calculated from a three-dimensional map of a voltageinflection point time Tdiff, a conduction time Ti, and a fuel pressure.

At S24, an error ratio is calculated in order to correct a requestedinjection quantity so as to reduce the difference between the requestedinjection quantity and an estimated injection quantity and the processproceeds to S25. The error ratio is a correction coefficient and iscalculated as a ratio of the sum of a corrected flow rate and a flowrate this time to a requested injection quantity. For example, an errorratio is calculated through the following expression (1). Here, thecorrected flow rate is a value obtained by dividing a requestedinjection quantity by a previous error ratio. An error flow rate is avalue representing a deviation and is the difference between a requestedinjection quantity and an estimated injection quantity.Error ratio K=Requested flow rate/{Corrected flow rate+Error flow ratethis time}=Requested flow rate/{(Requested flow rate/Previous errorratio)+Error flow rate this time}  (1)

At S25, whether or not an error ratio converges is determined and theprocess proceeds to S26 when the error ratio converges and the processfinishes when the error ratio does not converge. The case where theerror ratio converges means for example the case where a state ofkeeping an error ratio within a prescribed range lasts for a certainperiod of time. Since a previous error ratio is involved in thecalculation of an error ratio shown in the expression (1), a coefficientusable for correction can be set by making an error ratio converge.

At S26, since the error ratio converges, information showing that thecalculation of a correction coefficient required for correction by theelectromotive force quantity detection mode is completed is written in amemory and the process finishes. In other words, a flag showing thecompletion of the correction processing shown in FIG. 8 is written. As aresult, the correction processing is completed and the selectionprocessing shown in FIG. 6 can be executed.

Consequently, by correcting a requested injection quantity by using anerror ratio K, the requested injection quantity can come close to anestimated injection quantity. Specifically, a relationship between aninjection command pulse width Ti and an injection quantity Q is set byusing an error ratio. As a result, it is possible to: initially set arelationship between an injection command pulse width Ti and aninjection quantity Q corresponding to an injection characteristic of thefuel injection valve 10; and correct the relationship between theinjection command pulse width Ti and the injection quantity Q.Successively, by using a map defining the initially set relationshipbetween the injection command pulse width Ti and the injection quantityQ, a requested injection command pulse width Tireq corresponding to arequested injection quantity Qreq is calculated.

As explained above, in the fuel injection control device 20 according tothe present embodiment, the valve closing detection unit 54 can executeeither of the induced electromotive force quantity detection mode andthe timing detection mode. Consequently, the valve closing detectionunit 54 can be downsized further than a configuration of executing bothof the modes simultaneously. Further, the control circuit 21 functioningas a selection unit selects the timing detection mode when the ratio ofa requested injection quantity is equal to or larger than a referenceratio and selects the electromotive force quantity detection mode whenthe ratio of the requested injection quantity is smaller than areference ratio. The timing detection mode is superior to theelectromotive force quantity detection mode in detection accuracy buthas a detection range smaller than the electromotive force quantitydetection mode. In the case of a reference ratio or more that is in thedetection range of being detectable by the timing detection modetherefore, it is possible to select the timing detection mode and usethe timing detection mode suitably. Further, in the case of less than areference ratio that is in the detection range of not being detectableby the timing detection mode, the electromotive force quantity detectionmode is selected. Consequently, the electromotive force quantitydetection mode can make up for the narrow detection range of the timingdetection mode. As a result, a fuel injection device that can secureboth of the detection accuracy and the detection range of a valveclosing timing can be materialized.

Further, in the present embodiment, a requested injection quantity iscorrected so as to reduce the difference between an estimated injectionquantity estimated by using a valve closing timing detected by theelectromotive force quantity detection mode and the requested injectionquantity. Then the control circuit 21 functioning as a correction unituses a corrected value as a requested injection quantity for determiningwhether or not the timing detection mode is selected (refer to S1 inFIG. 6). Since the detection range of the timing detection mode isnarrow as stated earlier, an actual injection quantity may not be in thedetection range of the timing detection mode undesirably when thedifference between a requested injection quantity and the actualinjection quantity is large in the case of using the timing detectionmode. Consequently, the difference between a requested injectionquantity and an actual injection quantity is corrected firstly by usinga requested injection quantity estimated by using a valve closing timingof the electromotive force quantity detection mode having a widedetection range. As a result, the actual injection quantity can be inthe detection range of the timing detection mode by reducing thedifference between the requested injection quantity and the actualinjection quantity. It is therefore possible to switch the electromotiveforce quantity detection mode and the timing detection mode under anappropriate condition and make use of the mutual advantages of both thedetection modes while erroneous detection by the timing detection modeis suppressed.

Furthermore, in the present embodiment, the correction of theelectromotive force quantity detection mode is determined to becompleted when a state of keeping an error ratio of a requestedinjection quantity and an estimated injection quantity within aprescribed range lasts for a certain period of time. When an error ratioconverges in this way, the correction can be done by the converged errorratio. As a result, the correction can be done with a high degree ofaccuracy.

Moreover, in the present embodiment, an estimated injection quantity isestimated by using a valve closing timing and parameters having acorrelation with an actual injection quantity. As a result, theestimation accuracy of an estimated injection quantity can be improved.

In addition, in the present embodiment, an error ratio is calculated asa ratio of the sum of a corrected flow rate and an error quantity thistime to a requested injection quantity. A latest error ratio thereforeis calculated by using a previous error ratio. As a result, an errorratio can be calculated with a high degree of accuracy.

Still further, in the present embodiment, when a requested injectionquantity is not corrected by a correction coefficient, selection of thetiming detection mode is prohibited as shown at S5 in FIG. 6. As aresult, the timing detection mode is prevented from being executed outin the state of not initially corrected.

Yet further, in the present embodiment, a correction coefficient iscalculated when a prescribed detection condition is satisfied. An errormay be caused in an actual injection quantity and an appropriatecorrection may not be executed in some cases unless the detectioncondition is constant. By setting a detection condition therefore, it ispossible to calculate a correction coefficient under an identicalcondition and execute correction with a high degree of accuracy.

Additionally, in the present embodiment, a correction coefficient iscalculated when an injection interval of a prescribed time or longer issecured. As a result, an injection quantity can be inhibited fromdeviating by the influence of a residual magnetic force during previousinjection.

Other Embodiments

Although preferred embodiments of the present disclosure have beendescribed above, the present disclosure is not limited to theabove-described embodiments, and various modifications are contemplatedas exemplified below. The present disclosure is intended to covervarious modification and equivalent arrangements.

It should be understood that the configurations described in theabove-described embodiments are example configurations, and the presentdisclosure is not limited to the foregoing descriptions. In addition,while the various combinations and configurations, which are preferred,other combinations and configurations, including more, less or only asingle element, are also within the spirit and scope of the presentdisclosure. The scope of the present disclosure encompasses claims andvarious modifications of claims within equivalents thereof.

Although a detection mode is switched by using a ratio of a requestedinjection quantity and a reference ratio in the first embodiment statedearlier, the present disclosure is not limited to a configuration ofusing a reference ratio. For example, it is also possible to switch adetection mode by using a prescribed reference value. Specifically, itis also possible to: select the timing detection mode when a requestedinjection quantity is larger than a prescribed reference injectionquantity in partial lift injection; and select the electromotive forcequantity detection mode when the requested injection quantity is smallerthan the reference injection quantity. Since a process of calculating aratio is unnecessary in this way, the calculation load of the controlcircuit 21 can be reduced.

Although an error ratio is used for correction when the correction isexecuted in the first embodiment stated earlier, the present disclosureis not limited to a configuration of using an error ratio. For example,it is also possible to execute correction with a numerical valuerepresenting an error or another correction coefficient.

Although the fuel injection valve 10 is configured so as to have thevalve body 12 and the movable core 15 individually in the firstembodiment stated earlier, the fuel injection valve 10 may also beconfigured so as to have the valve body 12 and the movable core 15integrally. If they are configured integrally, the valve body 12 isdisplaced together with the movable core 15 in the valve openingdirection and shifts to valve opening when the movable core 15 isattracted.

Although the fuel injection valve 10 is configured so as to start theshift of the valve body 12 at the same time as the start of the shift ofthe movable core 15 in the first embodiment stated earlier, the fuelinjection valve 10 is not limited to such a configuration. For example,the fuel injection valve 10 may be configured so that: the valve body 12may not start valve opening even when the movable core 15 startsshifting; and the movable core 15 may engage with the valve body 12 andstart valve opening at the time when the movable core 15 moves by aprescribed distance.

The functions exhibited by the fuel injection control device 20 in thefirst embodiment stated earlier may be exhibited by hardware andsoftware, those being different from those stated earlier, or acombination of them. The control device for example may communicate withanother control device and the other control device may implement a partor the whole of processing. When a control device includes an electroniccircuit, the control device may include a digital circuit or an analogcircuit including many logic circuits.

While the present disclosure has been described with reference toembodiments thereof, it is to be understood that the disclosure is notlimited to the embodiments and constructions. The present disclosure isintended to cover various modification and equivalent arrangements. Inaddition, while the various combinations and configurations, othercombinations and configurations, including more, less or only a singleelement, are also within the spirit and scope of the present disclosure.

The invention claimed is:
 1. A fuel injection control device configuredto control a fuel injection valve including (i) a drive coil configuredto generate an electromagnetic attraction force, (ii) a movable coreconfigured to be attracted by the electromagnetic attraction force ofthe drive coil, and (iii) a valve body configured to separate from avalve seat and open a fuel passage by attracting the movable core from astate of contact with the valve seat at which the fuel passage isclosed, the fuel injection control device comprising an electroniccontrol unit (“ECU”) configured to: execute (i) full lift injection ofcontrolling the drive coil by an injection command pulse so as to allowa lift quantity of the valve body to reach a full lift position and (ii)partial lift injection of controlling the drive coil by an injectioncommand pulse so as to allow the lift quantity of the valve body not toreach the full lift position; detect, as a voltage value, change of aninduced electromotive force that is generated in the drive coil byintercepting an electric current supplied to the drive coil anddisplacing the valve body in a direction of valve closing; detect avalve closing timing when the valve body shifts to valve closing in thepartial lift injection by using either of (i) an electromotive forcequantity detection mode of detecting the valve closing timing bycomparing an accumulated quantity of the detected voltage values to aprescribed reference quantity and (ii) a timing detection mode ofdetecting an inflection point of a waveform of the detected voltagevalue; select either of the electromotive force quantity detection modeand the timing detection mode for detecting the valve closing timing;and calculate a correction coefficient for correcting a requestedinjection quantity so as to reduce a difference between an estimatedinjection quantity estimated by using the valve closing timing detectedby the electromotive force quantity detection mode and the requestedinjection quantity, wherein the ECU: selects the timing detection modewhen the requested injection quantity after being corrected by using thecorrection coefficient is larger than a prescribed reference injectionquantity in the partial lift injection, selects the electromotive forcequantity detection mode when the requested injection quantity afterbeing corrected by using the correction coefficient is smaller than thereference injection quantity, and selects the electromotive forcequantity detection mode regardless of a value of the requested injectionquantity when calculation of the correction coefficient is notcompleted.
 2. The fuel injection control device according to claim 1,wherein the ECU determines that the calculation of the correctioncoefficient is completed when a state of keeping an error ratio of therequested injection quantity after being corrected by using thecorrection coefficient and the estimated injection quantity within aprescribed range lasts for a certain period of time.
 3. The fuelinjection control device according to claim 1, wherein the ECU estimatesthe estimated injection quantity by using the valve closing timing andparameters having a correlation with an actual injection quantity. 4.The fuel injection control device according to claim 1, wherein the ECUprohibits the selection of the timing detection mode when the requestedinjection quantity is not corrected by the correction coefficient. 5.The fuel injection control device according to claim 1, wherein the ECUcalculates the correction coefficient when a prescribed detectioncondition is satisfied.
 6. The fuel injection control device accordingto claim 1, wherein the ECU calculates the correction coefficient whenan injection interval is a prescribed time or longer.